In the context of manufacturing fibre-reinforced parts, eg blades for a wind power plant, a manufacturing process is typically employed in which the blade is moulded in two halves in each their open mould, wherein a coat of gelcoat is initially applied onto the interior surface of the open mould. A number of layers of fibre material are subsequently arranged, following which resin is finally applied to attach the individual layers of fibre material to each other. The resin can be applied to the layers manually by RTM (resin transfer moulding), VARTM (vacuum assisted resin transfer moulding) or other suitable methods. Alternatively the resin can be applied to the laminate layers prior to laying of the layers (Prepeg). In the context of this, gelcoat will harden and form the blade surface.
In connection with such moulding process, the use of gelcoat is associated with major drawbacks with regard to the working environment, ia due to it having a large content of styrene, and ia during the hardening process inconvenient vapours are emitted. Therefore it is typically the case that robots are used in connection with application of gelcoat onto the interior surface of the mould, thereby enabling evacuation of staff from the moulding premises during the application process in order to thereby minimize the risk of the staff being exposed to the poor working conditions. However, typically further treatment will always be needed, and the presence of staff in relatively close contact with the gelcoat layer will always be required for the further process.
A further problem of gelcoat is that it is a brittle material and there is a risk of air pockets forming on the final surface. In connection with blades for wind turbines this may mean that water may collect in the pockets meaning that the blade is damaged in case a lightning strikes the blade.
Finally the gelcoat process as such is a very time-consuming one which is to be followed by a time-consuming cleaning of the equipment used for the application of gelcoat.
US 2004 0146714 teaches a method of manufacturing fibre-reinforced structures such as eg boat hulls, bathtubs, or car parts, wherein a thin composite hybrid layer of a thermoplastic acrylic polymer and a thermoplastic polymer are arranged distally followed by one or more fibre layers and optionally foam parts. The outermost hybrid layer which has good wear and cosmetic properties is formed initially by thermoforming processes in one mould and is then inserted into a second, closed mould along with fibre layer and foam parts, following which the mould is closed and resin injected. However, the dimensions of the thermoformed hybrid layer will unavoidably deviate from those of the fixed mould parts ia due to internal stresses in the layer and contractions following the thermoforming. This gives rise to difficulties in connection with the RTM-process where the strength of the connection between the various layers is reduced, and likewise the surface finish of the finished element may be scratched when the mould is closed.